Technologies
Multilateration
Multilateration (MLAT) is the process of locating aircraft based on the time difference of arrival (TDOA) of its transponder signal to three or more strategically placed receiver stations. A proven technology developed decades ago for the military, MLAT uses small, unmanned ground stations placed strategically around an airport or terminal to provide constant air traffic surveillance.
By determining the time difference of arrival (TDOA) of an aircraft's transponder signal to 3 or more receiver stations, an aircrafts exact location can be determined.
The stations listen for transponder returns or “reply” signals transmitted from local secondary surveillance radar (SSR) or MLAT stations. Because aircraft are located at different distances from each ground station, replies are received at fractionally different times. The stations send the data to a central data processor where sophisticated triangulation and TDOA computations provide the precise position of the aircraft.
Air traffic controllers see MLAT targets on their screens much the same as conventional targets. However, because MLAT data is updated every second, MLAT targets move at a much smoother and more accurate progression. By contrast, conventional SSRs must constantly rotate so position information is only updated once every 4-12 seconds, which gives radar targets the appearance of jumping across the screen. Of course, MLAT data can be slowed down to seamlessly integrate with existing SSR information.
MLAT requires no additional avionics equipment. It monitors Mode A, C and S transponders, as well as military IFF and ADS-B transponders. MLAT’s small, unmanned sensor stations are more accurate and less expensive than traditional SSRs and can be added to meet a wide range of coverage requirements and future surveillance needs.
Benefits
- Significantly lower in cost than traditional radar
- Easier and less costly to maintain and operate
- Enhanced performance that meets international standards
- Enables network expansion without changing basic equipment characteristics
- Extends the investment of air navigation service providers (ANSPs) and enables cost-sharing through expanded cross-border coverage
- Reduces environmental impact by utilizing a small footprint on existing structures